Rheumatoid Factor (RF)
Rheumatoid factor (RF) is a blood test that measures the amount of the RF antibody in the blood.
How the Test is Performed
Most of the time blood is typically drawn from a vein located on the inside of the elbow or the back of the hand.
In infants or young children, a sharp tool called a lancet may be used to puncture the skin.
- The blood collects in a small glass tube called a pipette, or onto a slide or test strip.
- A bandage is put over the spot to stop any bleeding.
How to Prepare for the Test
Most of the time you do not need to take special steps before this test.
How the Test Will Feel
You may feel slight pain or a sting when the needle is inserted. You may also feel some throbbing at the site after the blood is drawn.
Why the Test is Performed
This test is most often used to help diagnose rheumatoid arthritis or Sjogren syndrome.
Results are usually reported in one of two ways:
- Less than 40-60 u/mL
- Less than 1:80 (1 to 80) titer
A low number (normal result) usually means you do not have rheumatoid arthritis or Sjogren syndrome. However, some people who do have these conditions still have a "normal" or low rheumatoid factor (RF).
Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.
What Abnormal Results Mean
An abnormal result means the test is positive, which means higher levels of rheumatoid factor have been detected in your blood.
- Most patients with rheumatoid arthritis or Sjogren syndrome have positive RF tests.
- The higher the level, the more likely one of these conditions is present. There are also other tests for these disorders that help make the diagnosis.
- Not everyone with higher levels of rheumatoid factor has rheumatoid arthritis or Sjogren syndrome.
Your provider may do another blood test (anti-CCP antibody) to help diagnose rheumatoid arthritis.
People with the following diseases may also have higher levels of rheumatoid factor:
- Systemic lupus erythematosus
- Adult Still's disease
Higher-than-normal levels of RF may be seen in people with other medical problems. However, these higher RF levels cannot be used to diagnose these other conditions:
- AIDS, hepatitis, influenza, infectious mononucleosis, and other viral infections
- Certain kidney diseases
- Endocarditis, tuberculosis, and other bacterial infections
- Parasite infections
- Leukemia, multiple myeloma, and other cancers
- Chronic lung disease
- Chronic liver disease
In some cases, people who are healthy and have no other medical problem will have a higher-than-normal RF level.
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